Memory Test

5 min

Teacher Prep
Setup
Groups of 2. One copy of the data from the blackline master for each group.
Required Preparation
Provide one data set and one spinner for each student.

Narrative

In this activity, students review methods of obtaining samples that are fair and random. Students must make sense of the situation and will continue to work with the data to solve problems in later activities (MP1).

Launch

Arrange students in groups of 2. Each group gets both sets of data from the blackline master, one data set for each partner. Students will not need the spinners from the blackline master for this activity, but the spinners are included for use later in the lesson. Partners may work together to answer the questions, but should not share their data set with one another until told to do so in a later activity.

Student Task

Your teacher will give you a paper that lists a data set with 100 numbers in it. Explain whether each method of obtaining a sample of size 20 would produce a random sample.

Method 1: A spinner has 10 equal sections on it. Spin once to get the row number and again to get the column number for each member of your sample. Repeat this 20 times.

Method 2: Since the data looks random already, use the first two rows.

Method 3: Cut up the data and put them into a bag. Shake the bag to mix up the papers, and take out 20 values.

Method 4: Close your eyes and point to one of the numbers to use as your first value in your sample. Then, keep moving one square from where your finger is to get a path of 20 values for your sample.

Sample Response

  1. This would produce a random sample since each row and column has an equal chance of being selected.
  2. This would not produce a random sample since all of the values do not have an equal chance of being selected.
  3. This would produce a random sample since all the papers are the same size and each value has an equal chance of being selected.
  4. This would not produce a random sample since the path limits the values you can get in your sample. For example, the four corners could not all be in the same sample of 20.
Activity Synthesis (Teacher Notes)

The purpose of the discussion is to help students solidify their understanding of methods for selecting random samples.

Consider these questions for discussion:

  • “Can you think of other methods for selecting a random sample that are not listed here?” (Roll a polyhedron with 10 equal faces showing the numbers 1 through 10 to get the row, and roll again to get the column.)
  • “What do you need to look for when determining if a sample is random?” (Are all values equally likely to be included in the random sample?)
Standards
Addressing
  • 7.SP.1·Understand that statistics can be used to gain information about a population by examining a sample of the population; generalizations about a population from a sample are valid only if the sample is representative of that population. Understand that random sampling tends to produce representative samples and support valid inferences.
  • 7.SP.A.1·Understand that statistics can be used to gain information about a population by examining a sample of the population; generalizations about a population from a sample are valid only if the sample is representative of that population. Understand that random sampling tends to produce representative samples and support valid inferences.

10 min

10 min

5 min